Investigation of background sources associated with the production of radioactive isotopes in the DEVIS experiment (doub
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EMENTARY PARTICLES AND FIELDS Experiment
Investigation of Background Sources Associated with the Production of Radioactive Isotopes in the DEVIS Experiment (Double-Beta Decay) V. A. Belov* , O. Ya. Zeldovich** , and A. S. Kobyakin*** Institute of Theoretical and Experimental Physics, Bol’shaya Cheremushkinskaya 25, Moscow, 117289 Russia Received November 14, 2007
Abstract—Measurements performed in searches for the double-beta decay of 136 Xe showed an excess of events in exposures of a target enriched in the isotope 136 Xe in relation to exposures of a target depleted in this isotope. The activation of xenon in the detector used under the effect of background neutron and muon radiation and the possible contribution of these processes to the results of relevant measurements are studied. PACS numbers: 23.40.Bw DOI: 10.1134/S1063778808060069
In order to observe double-beta decay, use is made of the differential method, which makes it possible to
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Neutrinos play a key role in describing weakinteraction processes. Investigations of fundamental properties of the neutrino (its nature—a Dirac versus a Majorana neutrino—as well as the origin of neutrino masses and mixing) are of paramount importance for constructing physics beyond the Standard Model. Investigation of double-beta decay is one of the relevant lines of research here. Despite numerous experiments, 136 Xe doublebeta decay has not yet been detected. At the present time, the experimental lower limits on the half-life with respect to the two-neutrino channel are 8.5 × 1021 yr (according to experiments at Baksan Neutrino Observatory of the Institute for Nuclear Research [1]) and 1.1 × 1022 yr (according to DAMA measurements [2]) at a 90% confidence level. It should be noted that, for the isotope 130 Te, which is close to 136 Xe in parameters (matrix element and phase space), the half-life with respect to double-beta decay is substantially shorter, 7.6 × 1020 yr (NEMO [3]), and this calls for testing results on xenon. Measurement of the 136 Xe half-life with respect to the twoneutrino channel is also of importance in connection with the preparation of the EXO experiment [4], which will be aimed at searches for the neutrinoless decay channel. At the present time, the DEVIS experiment intended for exploring double-beta decay is being per-
formed at the Institute of Theoretical and Experimental Physics (ITEP, Moscow). In this experiment, a time-projection chamber (TPC) in a magnetic field is employed as a detector (TPC detector in a magnetic field—see Fig. 1). This facility makes it possible to use up to 10 kg of xenon at atmospheric pressure. The energy of electrons and the direction of their motion are determined by the shape of electron trajectories in a magnetic field. A detailed description of the facility is given elsewhere [5].
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1. INTRODUCTION
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E-mail: [email protected] E-mail: [email protected] *** E-mail: [email protected] **
Fig. 1. Layout of the facility.
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BELOV et al.
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